Bubble effect as a consequence of dielectric losses in cellulose insulation

The main reason of the research was to show the very important role of the dielectric losses in the insulation, during the initiation of water release from paper insulation, which is known as the bubble effect. The authors' thesis is that the dielectric losses increase in heavily moistened and aged cellulose insulation can cause dangerous temperature increase. The result of the temperature increase can be a dangerous bubble effect. The temperature increase caused by the dielectric losses in the paper insulation was called the thermal effect. The authors used samples of new and aged cellulose insulation for the research. The ageing extent of the paper samples was described by means of the cellulose polymerization degree. The ageing extent of the oil was described by means of the neutralization value. The authors investigated the influence of cellulose insulation ageing and moistening on dielectric losses. They also described conditions, i.e. insulation moistening and ageing, electric field intensity, which can lead to the thermal effect with the resulting bubble effect.